Interesting; I've been using WebAssembly as a compilation target for various projects for the past four years, and have been fairly happy with the state of documentation. I've never heard of that book you mentioned (I should check it out!), and instead I just read the spec directly: https://webassembly.github.io/spec/core/

Or occasionally I Google specific Wasm instructions and find .wat examples for them on MDN.

I'm sure you're right that the documentation is years behind that of HTML and CSS, but is there some specific aspect of Wasm documentation that you find lacking that isn't covered by the spec?